Starling Curve.
The amount of flow generated by the pump is determined by the pump speed and
by the pressure gradient that exists across the pump.“Pressure gradient” is defined
as the difference between the pressure at the pump outlet and pump inlet.
For a specified pump speed, flow varies inversely with pressure across the pump.
Therefore, increasing pump pressure differential (gradient) decreases flow, and
decreasing pump pressure differential increases flow. Hence, the dynamic parameter
that determines pump differential pressure is left ventricular pressure, which is
dependent upon the contractile state of the ventricle.
The simulated monitor tracings (
Figure 3
) show the ventricular and aortic pres-
sures of a patient:
·
The blue waveform represents the pressure at the pump inlet, which is the left
ventricular or LV pressure.
·
The red waveform represents the pressure at the pump outlet, which is the aor-
tic pressure.
·
The difference between these two pressures, indicated by the vertical yellow bar,
is the pressure difference across the pump. This difference varies over the car-
diac cycle, with the largest pressure difference occurring in ventricular diastole
and the smallest pressure difference occurring during ventricular systole.
CLINICAL OPERATION AND PATIENT MANAGEMENT
7
Figure 3
Tracings showing ventricular and aortic pressures
